Exhaust gas treatment system

ABSTRACT

A method and system for treating exhaust gas from stationary engines used to generate electricity is provided. Substantially all of the exhaust gases from at least one stationary combustion engine used for electrical power generation are collected and routed to an absorption tower. Inside the absorption tower the exhaust gases travel upwards in and through a plurality of perforated plates to a gas outlet in a top of the absorption tower. While the gas is ascending in the absorption tower, water is sprayed on the ascending gas and the perforated plates and this water is collected in the bottom of the absorption tower where at least some of it will be reused by spraying it back into the absorption tower to treat more exhaust gas from the combustion engines.

FIELD

The present invention relates to a system and method for treating exhaust gas and more particularly to a system and method for removing nitrous oxides, particulates and other pollutants from exhaust gas formed from the combustion of natural gas.

BACKGROUND

Existing fossil fuel power plants allow exhaust to be released into the atmosphere. In these emissions, oxides of nitrogen, carbon dioxide, sulfur dioxide and water vapor are all prime contributors to the greenhouse effect and could cause anthropogenic climate change. This technology would provide a useful means of capturing and diverting greenhouse effect contributors into a controllable liquid. While this is not a permanent sequestration, control of the resource is a fundamental first step in that process.

Additionally, fine carbon particulate is released during fossil fuel power production (esp. coal plants) and is a significant contributor to lung-related health problems and also causes negative environmental impacts such as acid rain and neutralizing glacial/arctic albedo.

SUMMARY OF THE INVENTION

In one aspect, a method for treating exhaust gas from stationary engines used to generate electricity is provided. The method comprises: capturing substantially all of the exhaust gases from at least one stationary combustion engine used for electrical power generation and routing substantially all of the exhaust gases to an absorption tower; allowing the exhaust gases to travel upwards in an interior of the absorption tower through a plurality of perforated plates to a gas outlet in a top end of the absorption tower; spraying water on the plurality of perforated plates and the exhaust gas as it travels upwards in the absorption tower; collecting water that was sprayed in the absorption tower in a bottom end of the absorption tower, the water containing nitrous oxides, sulfur dioxides and particulates removed from the exhaust gas; and reusing at least a portion of the water collected in the bottom end of the absorption tower to spray the at least a portion of the water back into the interior of the absorption tower.

In another aspect, a system for treating exhaust gas produced by combustion engines during the generation of electricity is provided. The system comprises: at least one stationary combustion engine adapted to generate electricity; an absorption tower, at least one exhaust conduit connecting the at least one stationary combustion engine to the absorption tower and operative to route substantially all of the exhaust gases from the at least one stationary combustion engine to an exhaust inlet of the absorption tower; and a sprayer system operatively connected to a water outlet of the absorption tower to route water from the absorption tower to a series of vertically spaced spray nozzles in the absorption tower. The absorption tower having an interior space, an exhaust inlet provided near a bottom end of the absorption tower, a gas outlet provided in a top end of the absorption tower, a plurality of plates provided in the interior of the absorption tower between the exhaust inlet and the gas outlet, each plate having a plurality of perforations, a series of vertically spaced spray nozzles, each spray nozzle directed into the interior of the absorption tower, and a water outlet provided proximate a bottom end of the absorption tower and below the exhaust inlet.

DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention is described below with reference to the accompanying drawings, in which:

FIG. 1 illustrates a schematic diagram of a system for treating exhaust gas from combustion engines used to produce electricity.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates a system for treating exhaust gases produced by one or more stationary combustion engines 10 that are used to produce electricity. Each stationary combustion engine 10 could be fueled by a range of acceptable fuels, but in one aspect each combustion engine 10 is fueled by natural gas. The system can capture the entire exhaust stream, remove contaminants from the exhaust stream and convert some of the output into transportable liquid products containing contaminants from the exhaust stream.

In the system, all of the exhaust gases from the one or more stationary combustion engines 10 are routed through at least one exhaust conduit 102 to an absorption tower 100 where the exhaust gas is treated. In an interior 108 of the absorption tower 100, the exhaust gas is allowed to pass upwards inside the absorption tower 100 as water is being sprayed on perforated plates 130 in the rising exhaust gas creating a chemical reaction binding the pollutants in the exhaust gas to the water before the treated exhaust gas exits the absorption tower 100. The water, now containing pollutants removed from the exhaust gas, will collect in the bottom of the absorption tower 100 where it can be removed by flowing naturally to a settling tank 254. Clean water from the settling tank 254 can then be pumped by a pump 250 through a filter and pH balance solution 252 to one or more coolant tanks 200 before at least some of the water is recirculated back into the absorption tank 100 to remove more pollutants from more exhaust gas that has been routed into the absorption tower 100.

As the combustion engines 10 operate they create exhaust gases containing the byproducts of the combustion of the fuel. All of these exhaust gases are collected from the combustion engines and directed to the absorption tower 100.

The combustion engines 10 can be natural gas fired combustion engines that would typically be used to generate electrical power. Natural gas is supplied to these combustion engines 10 and then combusted and used to produce electrical energy. The byproducts of this combustion from the burning of the natural gas are mainly carbon dioxide and water vapor, however, along with these main combustion byproducts there are also lesser amounts of carbon monoxide, sulfur dioxide, nitrogen oxides and particulates. The exhaust gas collected from the combustion engines 10 will contain these combustion byproducts. In this process, at this temperature, carbon monoxide bonds with oxygen and forms additional molecules of carbon dioxide.

As the exhaust gas exits each combustion engine 10 a temperature sensor 20 and a pressure sensor 30 can be used to measure the pressure and temperature of the exhaust gas exiting each combustion engine 100. Typically, this exhaust will have a temperature of between 410° C. and 480° C.

Optionally, the exhaust gas can then be routed to a heat exchanger 50 where the heat of the exhaust gas can be reduced to between 105° C. and 125° C. Another temperature sensor 60 and pressure sensor 70 can be provided after the heat exchanger 50 to measure the change in temperature and pressure of the exhaust gas as a result of it passing through the heat exchanger 50.

The cooled exhaust gases can be directed into the absorption tower 100 where they will be cooled to the correct chemical reaction temperature that will allow for pollutants such as the oxides of nitrogen (NO_(x)), particulates and engine oils will combine with the combustion produced water (H₂O) in the exhaust gas. The exhaust gases from the combustion engines 10 can be routed to the absorption tower 100 through one or exhaust conduits 102. The exhaust conduits 102 will collect the exhaust gases from the combustion engines 10 and run through a pipe or other conduit to the exhaust inlet 110 of the absorption tower 100. The heat exchanger 50 can be placed inline with the exhaust conduit 102. The exhaust conduit 102 can include an exhaust manifold so that a number of conduits running from each combustion engine 10 can be routed into a single pipe and conduit to be run to the exhaust inlet 110 of the absorption tower 100.

The exhaust gas can be introduced into the interior 108 of the absorption tower 100 through an exhaust inlet 110 provided near the bottom end of the absorption tower 100 but above a position where water would typically collect in the bottom of the absorption tower 100. The exhaust gases entering the absorption tower 100 will typically be in the range of 90° C. to 115° C. The exhaust gases can travel upwards in the absorption tower 100 from the exhaust inlet 110 towards a gas outlet 120 provided in the top of the absorption tower 100.

Between the exhaust inlet 110 and the gas outlet 120, a number of perforated plates 130 can be provided in conjunction with a number of spray nozzles 140. Each perforated plate 130 can have a number of perforations in the perforated plate 130 to allow water to drip through the perforations and gas to pass through the perforations in the perforated plate 130. In one aspect, the perforations can be a 1 inch hole in every 1 in² of perforate plate 130. The perforated plates 130 can be spaced vertically in the interior 108 of the absorption tower 100 and angled downwards to create a circuitous path for the exhaust gas to have to pass through before it can exit out of the gas outlet 120 provided at the top of the absorption tower 100. The spray nozzles 140 can be provided to spray water into the interior 108 of the absorption tower 100 and thereby onto exhaust gas that is ascending upwards through the absorption tower 100 and through the perforated plates 130. Additionally, the spray nozzles 140 can spray the water onto the perforated plates 130 causing some cooling of the perforated plates 130 since the perforated plates 130 will be constantly heated by the hot exhaust gas.

The water being sprayed in the interior 108 forms a bonding chemical reaction with the exhaust gases. The sprayed water can bond with the nitrous oxides, sulfur dioxides and particulate which will be absorbed into this sprayed water. The sprayed water will drop through the absorption tower 100 and collect in a bottom portion of the absorption tower 100. This collected water will contain nitrous oxides, sulfur dioxides and particulates that have been removed from the exhaust as it passes upwards through the absorption tower 100. Additionally 230 liters of water is produced for every 250E3 m³ of exhaust gases. An additional chemical reaction occurs at 120° C. which is the formation of CO₂ from the combination of CO and oxygen.

A water outlet 150 can be provided leading out of the lower portion of the absorption tower 100 to allow water that has collected in the lower portion of the absorption tower 100 to be removed to one or more settling tanks 254.

The absorption tower 100 can be provided with a level indicator 160 to determine the level of water that has collected in the bottom of the absorption tower 100 and a temperature sensor 162 to measure the temperature of the contents of the absorption tower 100.

A gas sensor 164 can be provided at the gas outlet 120 of the absorption tower 100 to measure the amount and type of gases exiting the absorption tower 100 through the gas outlet 120. Typically, the water sprayed into the interior 108 of the absorption tower 100 by the spray nozzles 140 will have removed a lot of, if not most of, the nitrous oxide, sulfur dioxide and particulates from the exhaust gas so the exiting gas will be mainly formed of CO₂ (carbon dioxide), O₂ (oxygen) and N₂ (Nitrogen). However, the gas sensor 164 can be used to ensure that the absorption tower 100 is operating properly and unwanted pollutants are not still present in the exiting gas.

The spray nozzles 140 can be part of a sprayer system 142 that sprays water into the absorption tower 100. A series of vertically spaced spray nozzles 140 can be provided where a pressurized water flow can be directed to them. The absorption tower 100 works by the water droplets combining with the exhaust gas. The surface area of the water droplets must be sufficient to meet the bonding requirements of the nitrogen oxide gases and the sulfur dioxide gases with the water molecules. Once the exhaust gas reaches between 70° C. and 90° C. the water vapor in the exhaust gas condenses rapidly and mixes with the water moving across the plates 130. NO₂, SO₂ and particulates are heavier than N₂ and O₂. The mixing reaction inside the absorption tower 100 can produce an acidic water mix with suspended particulates. The N₂, O₂ and CO₂ can move through the top of the absorption tower 100 with the water mix settling to the bottom end of the absorption tower 100.

The water that has collected in the bottom end of the absorption tower 100 can exit the absorption tower 100 through the water outlet 150 and then routed to at least one settling tank 254. The settling tank 254 can be equipped with level and temperature sensors and can be open to atmosphere on the top to help cool the water in the settling tank 254. In the settling tank 254, particulates suspended in the water can settle to the bottom of the settling tank 254 to be removed for sale. Oils from the engine combustion will naturally separate to the top of the water column, where they will be removed for recycling.

From the settling tank 254, the cleaned water can be taken through a filter and then brought back to a pH of 6.5 to 7.0 with a caustic injection system 252. This water can be sent to one or more cooling tanks 200 to bring the water temperature back down between 25° C. and 35° C. This process uses air movement across a number of spray nozzles 202. Typically the water entering the cooling tanks 200 will be in the range of 60° C. to 80° C. The water can be introduced into the cooling tanks 200 through spray nozzles 202 to cool the water before it is allowed to cool in the cooling tanks 200. A level sensor 210 can be provided to monitor the level of the water cooling in the cooling tanks 200.

Because one of the byproducts of the combustion of natural gas is water vapor, the water collected from the absorption tower 100 will likely be much greater than the amount needed to recirculate back to the spraying system 142 since some of this water will be from water vapor that has condensed out of the exhaust gas entering the exhaust inlet 110. Because of this, some of the water will usually be redirected for storage instead of being routed into the cooling tanks 200 and cooled before being recirculated back into the absorption tower 100 through the spraying system 142.

Because the nitrous oxides dissolved in the water can cause the water to become acidic, caustics may be added to the water to reduce the acidity of the water to a more neutral range. Test have indicated that the capture water is high in nitrogen and slightly acidic (pH of around 5.9), but does meet the guidelines for potable water for human consumption or industrial use. However, if it is desired to increase the pH to at or closer to a pH of 7, caustics can be added to the water.

From the cooling tank 200, the cooled water will typically be reduced in temperature to a range between 25° C. and 35° C. This cooled water can be routed to the spraying system 142 by a temperature sensor 220 to determine its temperature and a pressure sensor 222 to determine its pressure, before being routed to a pump 230 to be pressurized and sent to the spraying system 142 where it will once again be sprayed into the interior 108 of the absorption tower 100 through the spray nozzles 140.

The gas that exits the absorption tower 100 through the gas outlet 120 will be high in CO₂ and can be either exhausted to the atmosphere or sent for CO₂ extraction. In this further aspect, this treated gas can be routed to a CO₂ extraction unit 300 where the CO₂ can be removed from the gas and liquefied. A MEA absorption process can be used to remove CO₂ in the CO₂ extraction unit 300 which requires significant amounts of heat to break out the CO₂ after it is absorbed in the MEA solution. If the heat exchanger 50 is used, the present process produces the required heat to break out the CO₂ from the absorbed solution. The clean CO₂ then can be liquefied for sale back to the oil and gas industry for enhanced oil and gas recovery.

In one aspect, the complete process is a system where natural gas is used to produce electrical energy, then the exhaust gas, using the latent thermal energy can be turned into the following products: liquid carbon dioxide—used for enhanced oil and gas recovery; liquid distilled water—used in all industry processes; carbon particulates—used in many industrial applications; recycled oils—used to produce more refined oil; and clean emission stream of oxygen and nitrogen.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention. 

1. A method for treating exhaust gas from stationary engines used to generate electricity, the method comprising: capturing substantially all of the exhaust gases from at least one stationary combustion engine used for electrical power generation and routing substantially all of the exhaust gases to an absorption tower; allowing the exhaust gases to travel upwards in an interior of the absorption tower through a plurality of perforated plates to a gas outlet in a top end of the absorption tower; spraying water on the plurality of perforated plates and the exhaust gas as it travels upwards in the absorption tower; collecting water that was sprayed in the absorption tower in a bottom end of the absorption tower, the water containing nitrous oxides, sulfur dioxides and particulates removed from the exhaust gas; and reusing at least a portion of the water collected in the bottom end of the absorption tower to spray the at least a portion of the water back into the interior of the absorption tower.
 2. The method of claim 1 wherein the temperature of exhaust gas entering the absorption tower is from 90° C. to 115° C.
 3. The method of claim 1 further comprising cooling the exhaust gas rising through the interior of the absorption tower to a temperature from 70° C. to 90° C.
 4. The method of claim 1 further comprising cooling the exhaust gas to a temperature from 105° C. to 125° C. before routing the exhaust gas into the interior of the absorption tower.
 5. The method of claim 1 further comprising routing water collected in the bottom end of the absorption tower to a settling tank and allowing particles suspended in the water to settle out before reusing the at least a portion of the water to spray back into the interior of the absorption tower.
 6. The method of claim 1 further comprising cooling the at least a portion of the water to a temperature from 25° C. to 35° C. before spraying the at least a portion of the water back into the interior of the absorption tower.
 7. The method of claim 1 further comprising increasing the pH of the at least a portion of the water to a pH from 6.5 to 7.0 before spraying the at least a portion of the water back into the absorption tower.
 8. The method of claim 1 wherein the gas exiting the absorption tower is exhausted to the atmosphere.
 9. The method of claim 1 wherein the gas exiting the absorption tower is collected and routed for carbon dioxide extraction.
 10. A system for treating exhaust gas produced by combustion engines during the generation of electricity, the system comprising: at least one stationary combustion engine adapted to generate electricity; an absorption tower having: an interior space; an exhaust inlet provided near a bottom end of the absorption tower; a gas outlet provided in a top end of the absorption tower; a plurality of plates provided in the interior of the absorption tower between the exhaust inlet and the gas outlet, each plate having a plurality of perforations; a series of vertically spaced spray nozzles, each spray nozzle directed into the interior of the absorption tower; and a water outlet provided proximate a bottom end of the absorption tower and below the exhaust inlet, at least one exhaust conduit connecting the at least one stationary combustion engine to the absorption tower and operative to route substantially all of the exhaust gases from the at least one stationary combustion engine to the exhaust inlet of the absorption tower; and a sprayer system operatively connected to the water outlet of the absorption tower to route water from the absorption tower to the series of vertically spaced spray nozzles.
 11. The system of claim 10 wherein the at least one stationary combustion engine is natural gas fired.
 12. The system of claim 10 wherein the plurality of plates are angled downwards towards the bottom end of the absorption tower.
 13. The system of claim 12 wherein the series of vertically spaced spray nozzles are directed at the plurality of plates.
 14. The system of claim 10 wherein the plurality of plates forms a circuitous path that exhaust gas rising through the absorption tower from the exhaust inlet must pass through before exiting through the gas outlet
 15. The system of claim 10 further comprising a caustic injection system to increase the pH of water being routed to the series of vertically spaced spray nozzles.
 16. The system of claim 10 further comprising a settling tank connected to the water outlet so that water that has collected in the bottom end of the absorption tower is routed to the settling tank before being routed to the series of vertically spaced spray nozzles.
 17. The system of claim 16 further comprising at least one cooling tank to positioned after the settling tank in the system to cool the water to a temperature between 25° C. and 35° C. before routing the water to the series of vertically spaced spray nozzles.
 18. The system of claim 17 wherein the at least one cooling tank is a spray-type cooling tank.
 19. The system of claim 10 further comprising a heat exchanger provided inline of the at least one exhaust conduit to cool exhaust gas passing through the exhaust conduit.
 20. The system of claim 10 wherein the sprayer system includes a pump for pressurizing water being routed to the series of vertically spaced spray nozzles 